The Trouble With Hybrids

What is a hybrid?

In biology, the term hybrid has two meanings.

Different species hybrids
When two animals or plants of different taxa breed, the result is a hybrid. Hybrids between species belonging to different genera are referred to as intergeneric hybrids, while hybrids between different species belonging to the same genus are known as interspecific hybrids or crosses. Hybrids between different sub-species within a species are called intra-specific hybrids. It is very difficult for species belonging to different families to breed with each other, but it does happen occasionally and the result is known as an interfamilial hybrid.

Population/breed/cultivar hybrids
The second type of hybrid is crosses between different populations, breeds or cultivars within the same species. This type of hybrid is often intentionally produced by plant and animal breeders to promote and combine desirable characteristics. It is not a “true hybrid” in a biological sense of the world, but still very commonly used.

Why are hybrids created?

Hybrids can be produced due to many different reasons, and hybridization does occur in the wild as well. In captivity, one common reason for hybridization is the aquarist who tosses down closely related species into the same aquarium without caring about the risk of hybridization.

Hybridization can also be involuntarily as it can be really difficult to distinguish certain species from each other. Especially drab coloured females from various closely related species can be virtually impossible to tell apart from each other. If not even the male fish manages to tell the difference, it is certainly not easy for the aquarists.

There are also those who willingly produce hybrids since they want to create more appealing fish for the aquarium market, e.g. fish with striking colours and patterns or intricate finnage. In many cases these fishes will be openly marketed as hybrids, but there are also dishonest breeders who will try to pass them off as a new fascinating species or claim them to be a newly discovered population of one of the parent species.

Last but not least, hybrids can be produced when an aquarist really, really wants to breed his or her fish but fails to find a suitable mate from the same species. In such situation, some aquarists are tempted to try their luck with a closely related species instead.

What is the problem with hybrids?

A lot of fish species are today under threat of extinction in the wild and keeping them alive in aquariums is one way of preserving them for the future. This should naturally be combined with powerful environmental projects as well in order to preserve their natural habitats, but in the mean time captive breeding can be used to prevent species from vanishing from the planet. There are already numerous African cichlids that only survive in the hands of dedicated aquarists since they have become completely eradicated from the wild. Against this background, it is easy to see why hybridization can be a problem. If we have a rare African cichlid and allow it to breed with another species, we do not help preserving the rare species.

The situation becomes even more problematic when aquarists sell their hybrids as non-hybrids. Let’s say you want to help preserve a certain African cichlid by devoting time and energy to breeding it in captivity. If someone sells you a hybrid, claiming it to be a true purebred species, you will waste a lot of time and energy, and you may even dilute the gene pool further by crossing what you believe is a non-hybrid with specimens that actually are non-hybrids. Sooner or later, such as in the next generation or in the generation after that, you will end up with fish that look nothing like the African cichlid species you thought you were preserving. Some people erroneously believe that all hybrids are sterile, but this is very far from the truth, especially in fish.

Another problem has to do with rules and regulations regarding collection and import of live fish. When a species becomes endangered in the wild, it is common to ban harvest and marketing of that species in order to prevent the few remaining specimens from being removed from their natural habitat. Once a ban has been enforced, the aquarium hobby has to make do with specimens that have already entered the hobby. Using these specimens for hybridization is naturally not desirable.

Even fish that are not endangered in the wild can be hard to obtain, since your country or state may have a ban against it. Australia is for instance very strict when it comes to the import of foreign species, since Australia has experienced a tremendous amount of problems with invasive species from other parts of the world. Just as in the situation described above, the hobby then has to make do with specimens that have already been imported and using these specimens for hybridization can cause the species to vanish entirely from the local hobby.

Different populations

Different populations within the same species can be very dissimilar. This can for instance be seen in Lake Malawi cichlids where two populations of the same species living just a few hundred meters apart can look highly disparate. If we want to preserve the distinctness of each population, we must refrain from mixing fish from different populations in the aquarium. It is therefore recommended to work within each population and only breed fish hailing from the same area.

What can I do?

Do not keep closely related species in the same aquarium.

Do not mix distinct populations of the same species.

Try to find out the ancestry of your fish before you start breeding them. This is especially important when breeding rare fish species. Comparing the fish with pictures and descriptions of wild fish is always recommended. Do not be afraid to contact other experienced aquarists and ask for their opinion before you allow the fish to breed.

Be suspicious when “new” species of fish suddenly enter the market – they can be hybrids that someone is trying to pass of as a new species. The same thing is true for species that has to be smuggled into your country; dishonest aquarists can produce hybrids that look similar to the banned species and try to sell them to aquarists who are willing to purchase illegally imported fish.

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